The objective of this project is to elucidate the morphological basis for elongation and contraction in teleost retinal cone cells and to specify some of the physiological parameters of these processes. Teleost cones elongate in darkness and contract in light; cell shape change is simple, linear, cyclic and triggered by light conditions. The project includes 1) ultrastructural studies of the changes in distribution of acting and myosin filaments during contraction, 2) rate studies of cone contraction in cultured retinal slices, 3) contractile models of cones in retinal slices and as isolated cones, 4) SDS gel electrophoretic analysis of motility proteins in isolated cones, 5) fluorescent antibody localization of myosin in isolated cones and retinal slices, 6) studies of temperature and D2O effects on cone elongation in cultured retinal slices, and 7) motile models of elongating cones in retinal slices and as isolated cones. Techniques include TEM, time-lapse cinematography and TV-monitoring for ascertaining rates of cone contraction in retinal slices viewed with Nomarski optics and SDS gel electrophoresis.